gstlal-inspiral TESTS not included in tarballs

gstlal-inspiral's python TESTS scripts (from /gstlal-inspiral/tests/Makefile.am) aren't included in the EXTRA_DIST list, which means they aren't being included in the release distributions, which in turn results in build failures when executing make check from a source build:

make  check-TESTS
make[2]: Entering directory '$SRC_DIR/_build/tests'
make[3]: *** No rule to make target 'stats_horizonhistory_verify.py', needed by 'stats_horizonhistory_verify.py.log'.  Stop.